The present invention relates to a contactless IC card mounting IC chip having analog, digital, and memory circuits on the IC chip.
A contactless IC card mounts antenna coils and IC chips and communicates with a terminal called a reader/writer by wireless to implement various functions such as authentication.
Electric power for driving the IC chip is obtained by receiving an electromagnetic wave transmitted from the reader/writer.
FIG. 7 shows an IC chip for a contactless IC card according to the prior art.
In FIG. 7, reference number 1 denotes an antenna coil, 2 denotes a resonance capacitance, 3 denotes a rectifier circuit, 4 denotes a smoothing capacitance, 5 denotes a analog circuit, 6 denotes a digital circuit, 7 denotes a memory control circuit, and 8 denotes a memory circuit.
An electromagnetic wave transmitted from the reader/writer is received by the antenna coil 1. The resonance capacitance 2 is connected to the antenna coil 1 in parallel so as to resonate at the frequency of the electromagnetic wave. An AC signal received by the antenna coil 1 is converted into a DC signal by the rectifier circuit 3. The smoothing capacitance 4 is connected in parallel across the outputs VDD-VSS of the rectifier circuit 3 and smoothes a rectified ripple waveform. The outputs VDD and VSS of the rectifier circuit are connected to the analog circuit 5, digital circuit 6, memory control circuit 7, and memory circuit 8.
The analog circuit 5 comprises components such as a demodulator circuit for decoding receive data superimposed on the carrier of the electromagnetic wave and a modulator circuit for superimposing a transmission signal generated by the digital circuit 6 on the carrier of the electromagnetic wave.
The digital circuit 6 comprises components such as a CPU for performing various digital signal processes. The memory control circuit 7 controls the operation of the memory circuit 8. The memory circuit 8 is nonvolatile memory.
The nonvolatile memory requires a relatively high power-supply voltage (VDD=5 volts) in order to ensure the retention of data written in memory cells. On the other hand, the analog circuit 5, digital circuit 6, and memory control circuit 7 today require lower power-supply voltages (VDD=2.5 to 3.3 volts) because their transistors have been miniaturized. The prior-art IC chip for contactless IC card is capable of operating at a power-supply voltage VDD of over approximately 5 volts.
In the prior-art IC chip for a contactless IC card as described above, a minimum value of a power-supply voltage VDD at which the IC chip can be operated is limited by a minimum value of a voltage (VDD=5 volts) at which a memory circuit 8 can be operated because an analog circuit 5, a digital circuit 6, a memory control circuit 7, and the memory circuit 8 share a common power supply.
Therefore, the IC chip cannot be operated at a lower voltage and a communication distance to a reader/writer cannot be increased.
In addition, power-supply noise generated during the operation of the memory circuit 8 propagates to the analog circuit 5 to cause malfunctions in circuits such as a demodulator circuit. The power-supply noise can be reduced by increasing capacity of a smoothing capacitance 4. However, it is difficult to increase the capacity to such an extent that the power-supply noise can be eliminated, because the decoding capability of the demodulator circuit in the analog circuit 5 is decreased.
It is an object of the present invention to provide an IC chip for a contactless IC card that ensures reliability in data retention of nonvolatile memory and the like, and consumes lower power.
It is another object of the present invention to provide an IC chip for a contactless IC card that can prevent malfunctions in other circuits due to power-supply noise during an operation of a memory circuit.
An IC chip for a contactless IC card according to aspect 1 of the present invention is an IC chip for a contactless IC card for rectifying and smoothing a signal provided contactlessly from an external source to feed required electric power to internal signal processing circuits and a memory circuit to read and write data to and from that memory circuit, wherein the signal provided contactlessly from the external source is rectified, smoothed and provided to the signal processing circuits and the signal provided contactlessly from the external source is boosted by a booster circuit and provided to the memory circuit.
According to this configuration, the booster circuit is provided to cause the memory circuit having nonvolatile memory to operate at a boosted voltage and the other circuits to operate at a lower voltage, thus enabling lowered power consumption while ensuring the reliability in data retention of the nonvolatile memory and the like. In addition, because the power supply line for the memory circuit is separated from the power supply lines for the other circuits, malfunctions in the other circuits due to power-supply noise during memory circuit operation can be prevented.
The IC chip for contactless IC card according to aspect 2 of the present invention is characterized in that the memory according to aspect 1 is a ferroelectric memory.
The IC chip for contactless IC card according to aspect 3 of the present invention is characterized in that in aspect 1, the booster circuit boosts an output voltage output by rectifying and smoothing the signal provided contactlessly from the external source by switching the output voltage by using a clock signal repeatedly outputted, and charges a storage capacitance with the boosted output to supply power to the memory circuit.
The IC chip for contactless IC card according to aspect 4 is characterized in that in aspect 3, a resistance is inserted in series in a charging circuit from the boosted output to the storage capacitance to supply power from the storage capacitance to the memory circuit.
According to this configuration, a resistance provided between a boosted voltage output terminal and a storage capacitance produces a difference in impedance, and this difference facilitates a current supply from the storage capacitance to the memory circuit, thereby preventing malfunctions in the other circuits due to power-supply noise during a memory circuit operation even when the memory circuit operates and instantaneously consumes a high current.
The IC chip for a contactless IC card according to aspect 5 is characterized in that in aspect 3, the storage capacitance is charged by the output boosted by the booster circuit to supply power to the memory circuit, and that a boosting operation is stopped by detecting that the output voltage from the booster circuit exceeds a predetermine voltage, and the boost operation is automatically restarted by detecting that the output voltage drops below the predetermined voltage.
According to this configuration, power consumption can be reduced because the voltage boosting operation is stopped when the boosted voltage exceeds a predetermined voltage. In addition, since the boosted voltage does not become higher than the predetermined voltage, deterioration of devices due to excessive boosting can be prevented.